1. Field of the Invention
The present invention relates to a printer for forming an image on a continuous-form recording sheet using an electrophotographic method.
2. Background and Material Information
There have been conventionally known image forming apparatuses using the so-called electrophotographic method, such as with an electronic copying machine, in which an electrostatic latent image is formed by exposing a photoreceptor on the surface of a charged photoconductive drum. Toner is adhered to the latent image for development, then transferred to a recording sheet arranged to be synchronously fed with the photoconductive drum and thereafter fixed by a fixing unit.
Another example is a laser beam printer arranged so as to obtain a hard copy of image information by scanning and exposing a charged photoconductive drum by modulated laser beams, based on the image to be developed (including figures, characters and the like), using the copy process of the above electrophotographic method.
The laser beam printer is very useful and versatile, because it can be used to draw figures of information received by an image reading unit, such as an image scanner, or used to output information at a high speed.
In general, such a laser beam-printer is based upon a conventional well-known electronic copying machine, and employs pre-cut individual sheets, which are cut into predetermined sizes, as a recording medium on which the desired image is formed. A so-called heat roller-type fixing unit, which has a pair of fixing rollers including a heat roller arranged to be heated with high temperatures, and a backup roller arranged to be brought into contact with the heat roller at a predetermined pressure force, is utilized. The recording medium, on which an unfixed toner image corresponding to the image information is formed, is caused to pass between the rollers so that it is heated and pressed, whereby the toner is melted and adhered on the recording medium, causing the desired image to be formed and fixed on the surface of the recording medium.
The electrophotographic method is used, that is, the rotation of a photoconductive drum causes an exposed portion thereof to reach a transfer unit, thereafter a toner image is transferred onto the recording sheet which is fed at a predetermined speed which is identical with the peripheral speed of the photoconductive drum at the transfer unit. Thus, in this process, it is impossible to form images intermittently by interrupting the process.
Therefore, the laser beam printer is provided with a memory capable of storing image information data for at least one page, and when the image information data for one page is completely input therein, the printer outputs the data one page at a time.
This laser beam printer can be used as an output terminal of a computer. In this case, the continuous-form sheet, similar to that having been used in a conventional line printer, is used. The continuous-form sheet, hereinafter, simply referred to as a "continuous sheet", used in the conventional line printer is a so-called fan-folded sheet having a plurality of sprocket holes provided at both side edges, at a predetermined interval along the longitudinal direction thereof, and arranged to be folded along perforated tear lines to enable the sheet to be readily cut off.
When a continuous sheet is employed in a laser beam printer that utilizes a heat roll fixing system, the length of the recording sheet feed path, from a transferring position of a transferring unit to a fixing position of a fixing unit, must be set to substantially equal the distance between the perforated tear lines of the continuous sheet, in order to prevent such a problem occurs as when the laser beam printer stops feeding the continuous sheet after the image forming operation, and a page, stopped during the fixing operation, is held between the pair of fixing rollers. Thus, unfixed toner, used in the process of the fixing operation, remains caught between the pair of the fixing rollers.
More specifically, since the continuous sheet is finally cut off along the perforated tear lines for use, no image must be formed within a predetermined region in the vicinity of the perforated tear lines. Thus, in a laser beam printer by which images are formed for each page, the vicinity of the tear lines, where no image is formed, is arranged to be stopped at the transferring position of the transferring unit. Consequently, when the length of the recording sheet feed path, from the transferring position to the fixing position, is set to substantially equal the distance between the perforated tear lines of the continuous sheet, the above problem can be avoided, because the vicinity of the tear lines, where no image is formed, is caused to be located at the fixing position at the fixing unit where the action is effected, when the laser beam printer stops to feed the continuous sheet.
As a result, however, a problem arises in that the printer as a whole is made unnecessarily large in size to provide the necessary feed length for the recording sheet. A plurality of different kinds of continuous sheets, respectively, having a different distance between perforated tear lines (i.e., a length of a page), cannot be interchangeably used in this type of laser beam printer (i.e., continuous sheets having a different distance between perforated tear lines cannot be used).
Furthermore, it is necessary to additionally feed the continuous sheet, at least, in an amount corresponding to one page in order to execute the fixing operation on the last page. Moreover, it is necessary to feed the continuous sheet in an amount corresponding to one page without an image forming operation in order to completely discharge the continuous sheet, on which the image forming operations have been executed, from the laser beam printer. Thus, the continuous sheet may be wasted.